Curing substrate pretreatment compositions in nanoimprint lithography

ABSTRACT

A nanoimprint lithography method includes disposing a pretreatment composition on a nanoimprint lithography substrate to form a pretreatment coating, and disposing discrete portions of imprint resist on the pretreatment coating, each discrete portion of the imprint resist covering a target area of the nanoimprint lithography substrate. The imprint resist is a polymerizable composition and includes a polymerization initiator. A composite polymerizable coating is formed on the nanoimprint lithography substrate as each discrete portion of the imprint resist spreads beyond its target area. The composite polymerizable coating is contacted with a nanoimprint lithography template. The polymerization initiator is activated, and the composite polymerizable coating is polymerized to yield a composite polymeric layer and an uncured portion of the pretreatment coating on the nanoimprint lithography substrate. After polymerizing the composite polymerizable coating to yield the composite polymeric layer, the uncured portion of the pretreatment coating is polymerized.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Patent Application Ser. No.62/316,377 entitled “CURING SUBSTRATE PRETREATMENT COMPOSITIONS INNANOIMPRINT LITHOGRAPHY” and filed on Mar. 31, 2016, which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

This invention relates to curing a substrate pretreatment composition ina nanoimprint lithography process, as well as pretreatment compositionssuitable for curing independently of an imprint resist.

BACKGROUND

As the semiconductor processing industry strives for larger productionyields while increasing the number of circuits per unit area, attentionhas been focused on the continued development of reliablehigh-resolution patterning techniques. One such technique in use todayis commonly referred to as imprint lithography. Imprint lithographyprocesses are described in detail in numerous publications, such as U.S.Patent Application Publication No. 2004/0065252, and U.S. Pat. Nos.6,936,194 and 8,349,241, all of which are incorporated by referenceherein. Other areas of development in which imprint lithography has beenemployed include biotechnology, optical technology, and mechanicalsystems.

An imprint lithography technique disclosed in each of the aforementionedpatent documents includes formation of a relief pattern in an imprintresist and transferring a pattern corresponding to the relief patterninto an underlying substrate. The patterning process uses a templatespaced apart from the substrate and a polymerizable composition (an“imprint resist”) disposed between the template and the substrate. Insome cases, the imprint resist is disposed on the substrate in the formof discrete, spaced-apart drops. The drops are allowed to spread beforethe imprint resist is contacted with the template. After the imprintresist is contacted with the template, the resist is allowed touniformly fill the space between the substrate and the template, thenthe imprint resist is solidified to form a layer that has a patternconforming to a shape of the surface of the template. Aftersolidification, the template is separated from the patterned layer suchthat the template and the substrate are spaced apart.

Throughput in an imprint lithography process generally depends on avariety of factors. When the imprint resist is disposed on the substratein the form of discrete, spaced-apart drops, throughput depends at leastin part on the efficiency and uniformity of spreading of the drops onthe substrate. Spreading of the imprint resist may be inhibited byfactors such as gas voids between the drops and incomplete wetting ofthe substrate and/or the template by the drops.

Throughput in an imprint lithography process may be improved bypretreating the substrate with a pretreatment composition thatfacilitates spreading of the imprint resist. However, presence ofuncured pretreatment composition after completing the imprintlithography process may cause defects in the resulting patterned layersif the pretreatment composition is allowed to spread onto imprintedfields, and may result in contamination by evaporating from thesubstrate.

SUMMARY

In a first general aspect, a nanoimprint lithography method includesdisposing a pretreatment composition on a nanoimprint lithographysubstrate to form a pretreatment coating on the nanoimprint lithographysubstrate and disposing discrete portions of imprint resist on thepretreatment coating, each discrete portion of the imprint resistcovering a target area of the nanoimprint lithography substrate. Thepretreatment composition includes a polymerizable component. The imprintresist is a polymerizable composition and includes a polymerizationinitiator. A composite polymerizable coating is formed on thenanoimprint lithography substrate as each discrete portion of theimprint resist spreads beyond its target area. The compositepolymerizable coating includes a mixture of the pretreatment compositionand the imprint resist. The composite polymerizable coating is contactedwith a nanoimprint lithography template. The polymerization initiator isactivated, and the composite polymerizable coating is polymerized toyield a composite polymeric layer and an uncured portion of thepretreatment coating on the nanoimprint lithography substrate. Afterpolymerizing the composite polymerizable coating to yield the compositepolymeric layer, the uncured portion of the pretreatment coating ispolymerized.

A second general aspect include a nanoimprint lithography stack formedby the method of the first general aspect.

Implementations of the first and second general aspect may include oneor more of the following features.

In some embodiments, the pretreatment composition is free orsubstantially free of a polymerization initiator.

In some cases, the polymerization initiator includes a firstphotoinitiator, and polymerizing the composite polymerizable coatingincludes initiating polymerization of the composite polymerizablecoating by irradiating the composite polymerizable coating with UVradiation of a first wavelength, intensity, energy density, andduration. The pretreatment composition may be free of a polymerizationinitiator. Polymerizing the uncured portion of the pretreatment coatingmay include irradiating the uncured portion of the pretreatment coatingwith UV radiation of the first wavelength and a second intensity, energydensity, duration, or combination thereof, where at least one of thesecond intensity, energy density, or duration differs from that of thefirst and is sufficient to initiate autopolymerization of the uncuredportion of the pretreatment composition.

In certain cases, the pretreatment composition includes a thermalinitiator. Polymerizing the uncured portion of the pretreatment coatingmay include heating the uncured portion of the pretreatment coating to atemperature and for a duration sufficient to initiate polymerization ofthe uncured portion of the pretreatment coating.

The imprint resist may include a photosensitizer. The pretreatmentcomposition may include the first photoinitiator. Polymerizing theuncured portion of the pretreatment coating may include irradiating theuncured portion of the pretreatment coating with UV radiation of thefirst wavelength and a second intensity, energy density, duration, orcombination thereof, wherein at least one of the second intensity andenergy density exceeds that of the first.

In some cases, the pretreatment coating includes a secondphotoinitiator. The second photoinitiator may be different from thefirst photoinitiator. Polymerizing the uncured portion of thepretreatment coating may include irradiating the uncured portion of thepretreatment coating with UV radiation of a second wavelength, where thesecond wavelength is shorter than the first wavelength. Polymerizing theuncured portion of the pretreatment coating may include irradiating theuncured portion of the pretreatment coating with UV radiation of asecond wavelength and a second intensity, energy density, or duration,wherein the second wavelength is shorter than the first wavelength, andat least one of the second intensity and energy density exceeds that ofthe first. Polymerizing the uncured portion of the pretreatment coatingmay include irradiating the uncured portion of the pretreatment coatingwith UV radiation of a second intensity, energy density, or duration,wherein at least one of the second intensity or energy density exceedsthat of the first.

In certain cases, activating the polymerization initiator does notinitiate polymerization of the pretreatment composition.

The details of one or more implementations of the subject matterdescribed in this specification are set forth in the accompanyingdrawings and the description below. Other features, aspects, andadvantages of the subject matter will become apparent from thedescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a simplified side view of a lithographic system.

FIG. 2 depicts a simplified side view of the substrate shown in FIG. 1,with a patterned layer formed on the substrate.

FIGS. 3A-3D depict spreading interactions between a drop of a secondliquid on a layer of a first liquid.

FIG. 4 is a flowchart depicting a process for facilitating nanoimprintlithography throughput.

FIG. 5A depicts a nanoimprint lithography substrate. FIG. 5B depicts apretreatment coating disposed on a nanoimprint lithography substrate.

FIGS. 6A-6D depict formation of a composite coating from drops ofimprint resist disposed on a substrate having a pretreatment coating.

FIGS. 7A-7D depict cross-sectional views along lines w-w, x-x, y-y, andz-z of FIGS. 6A-6D, respectively.

FIGS. 8A and 8B depict cross-sectional views of a pretreatment coatingdisplaced by drops on a nanoimprint lithography substrate.

FIGS. 9A-9C depict cross-sectional views of a template in contact with ahomogeneous composite coating and the resulting nanoimprint lithographystack.

FIGS. 10A-10C depict cross-sectional views of a template in contact withan inhomogeneous composite coating and the resulting nanoimprintlithography stack.

FIG. 11 depicts a nanoimprint lithography substrate with a compositepolymeric layer and uncured pretreatment coating

FIGS. 12A-12C are flowcharts depicting processes for polymerizing anuncured pretreatment composition independently of a compositepolymerizable coating.

FIG. 13 is an image of drops of an imprint resist after spreading on anadhesion layer of a substrate without a pretreatment coating,corresponding to Comparative Example 1.

FIG. 14 is an image of drops of an imprint resist after spreading on apretreatment coating as described in Example 1.

FIG. 15 is an image of drops of an imprint resist after spreading on apretreatment coating as described in Example 2.

FIG. 16 is an image of drops of an imprint resist after spreading on apretreatment coating as described in Example 3.

FIG. 17 shows defect density as a function of prespreading time for theimprint resist and pretreatment of Example 2.

FIG. 18 shows drop diameter versus time for spreading pretreatmentcompositions.

FIG. 19A shows viscosity as a function of fractional composition of onecomponent in a two-component pretreatment composition. FIG. 19B showsdrop diameter versus time for various ratios of components in atwo-component pretreatment composition. FIG. 19C shows surface tensionof a two-component pretreatment composition versus fraction of onecomponent in the two-component pretreatment composition.

DETAILED DESCRIPTION

FIG. 1 depicts an imprint lithographic system 100 of the sort used toform a relief pattern on substrate 102. Substrate 102 may include a baseand an adhesion layer adhered to the base. Substrate 102 may be coupledto substrate chuck 104. As illustrated, substrate chuck 104 is a vacuumchuck. Substrate chuck 104, however, may be any chuck including, but notlimited to, vacuum, pin-type, groove-type, electromagnetic, and/or thelike. Exemplary chucks are described in U.S. Pat. No. 6,873,087, whichis incorporated by reference herein. Substrate 102 and substrate chuck104 may be further supported by stage 106. Stage 106 may provide motionabout the x-, y-, and z-axes. Stage 106, substrate 102, and substratechuck 104 may also be positioned on a base.

Spaced apart from substrate 102 is a template 108. Template 108generally includes a rectangular or square mesa 110 some distance fromthe surface of the template towards substrate 102. A surface of mesa 110may be patterned. In some cases, mesa 110 is referred to as mold 110 ormask 110. Template 108, mold 110, or both may be formed from suchmaterials including, but not limited to, fused silica, quartz, silicon,silicon nitride, organic polymers, siloxane polymers, borosilicateglass, fluorocarbon polymers, metal (e.g., chrome, tantalum), hardenedsapphire, or the like, or a combination thereof. As illustrated,patterning of surface 112 includes features defined by a plurality ofspaced-apart recesses 114 and protrusions 116, though embodiments arenot limited to such configurations. Patterning of surface 112 may defineany original pattern that forms the basis of a pattern to be formed onsubstrate 102.

Template 108 is coupled to chuck 118. Chuck 118 is typically configuredas, but not limited to, vacuum, pin-type, groove-type, electromagnetic,or other similar chuck types. Exemplary chucks are further described inU.S. Pat. No. 6,873,087, which is incorporated by reference herein.Further, chuck 118 may be coupled to imprint head 120 such that chuck118 and/or imprint head 120 may be configured to facilitate movement oftemplate 108.

System 100 may further include a fluid dispense system 122. Fluiddispense system 122 may be used to deposit imprint resist 124 onsubstrate 102. Imprint resist 124 may be dispensed upon substrate 102using techniques such as drop dispense, spin-coating, dip coating,chemical vapor deposition (CVD), physical vapor deposition (PVD), thinfilm deposition, thick film deposition, or the like. In a drop dispensemethod, imprint resist 124 is disposed on substrate 102 in the form ofdiscrete, spaced-apart drops, as depicted in FIG. 1.

System 100 may further include an energy source 126 coupled to directenergy along path 128. Imprint head 120 and stage 106 may be configuredto position template 108 and substrate 102 in superimposition with path128. System 100 may be regulated by a processor 130 in communicationwith stage 106, imprint head 120, fluid dispense system 122, and/orsource 126, and may operate on a computer readable program stored inmemory 132.

Imprint head 120 may apply a force to template 108 such that mold 110contacts imprint resist 124. After the desired volume is filled withimprint resist 124, source 126 produces energy (e.g., electromagneticradiation or thermal energy), causing imprint resist 124 to solidify(e.g., polymerize and/or crosslink), conforming to the shape of surface134 of substrate 102 and patterning surface 112. After solidification ofimprint resist 124 to yield a polymeric layer on substrate 102, mold 110is separated from the polymeric layer.

FIG. 2 depicts nanoimprint lithography stack 200 formed by solidifyingimprint resist 124 to yield patterned polymeric layer 202 on substrate102. Patterned layer 202 may include a residual layer 204 and aplurality of features shown as protrusions 206 and recesses 208, withprotrusions 206 having a thickness t₁ and residual layer 204 having athickness t2. In nanoimprint lithography, a length of one or moreprotrusions 206, recessions 208, or both parallel to substrate 102 isless than 100 nm, less than 50 nm, or less than 25 nm. In some cases, alength of one or more protrusions 206, recessions 208, or both isbetween 1 nm and 25 nm or between 1 nm and 10 nm.

The above-described system and process may be further implemented inimprint lithography processes and systems such as those referred to inU.S. Pat. Nos. 6,932,934; 7,077,992; 7,197,396; and 7,396,475, all ofwhich are incorporated by reference herein.

For a drop-on-demand or drop dispense nanoimprint lithography process,in which imprint resist 124 is disposed on substrate 102 as discreteportions (“drops”), as depicted in FIG. 1, the drops of the imprintresist typically spread on the substrate 102 before and after mold 110contacts the imprint resist. If the spreading of the drops of imprintresist 124 is insufficient to cover substrate 102 or fill recesses 114of mold 110, polymeric layer 202 may be formed with defects in the formof voids. Thus, a drop-on-demand nanoimprint lithography processtypically includes a delay between initiation of dispensation of thedrops of imprint resist 124 and initiation of movement of the mold 110toward the imprint resist on the substrate 102 and subsequent filling ofthe space between the substrate and the template. Thus, throughput of anautomated nanoimprint lithography process is generally limited by therate of spreading of the imprint resist on the substrate and filling ofthe template. Accordingly, throughput of a drop-on-demand or dropdispense nanoimprint lithography process may be improved by reducing“fill time” (i.e., the time required to completely fill the spacebetween the template and substrate without voids). One way to decreasefill time is to increase the rate of spreading of the drops of theimprint resist and coverage of the substrate with the imprint resistbefore movement of the mold toward the substrate is initiated. Asdescribed herein, the rate of spreading of an imprint resist and theuniformity of coverage of the substrate may be improved by pretreatingthe substrate with a liquid that promotes rapid and even spreading ofthe discrete portions of the imprint resist and polymerizes with theimprint resist during formation of the patterned layer.

Spreading of discrete portions of a second liquid on a first liquid maybe understood with reference to FIGS. 3A-3D. FIGS. 3A-3D depict firstliquid 300 and second liquid 302 on substrate 304 and in contact withgas 306 (e.g., air, an inert gas such as helium or nitrogen, or acombination of inert gases). First liquid 300 is present on substrate304 in the form of coating or layer, used here interchangeably. In somecases, first liquid 300 is present as a layer having a thickness of afew nanometers (e.g., between 1 nm and 15 nm, or between 5 nm and 10nm). Second liquid 302 is present in the form of a discrete portion(“drop”). The properties of first liquid 300 and second liquid 302 mayvary with respect to each other. For instance, in some cases, firstliquid 300 may be more viscous and dense than second liquid 302.

The interfacial surface energy, or surface tension, between secondliquid 302 and first liquid 300 is denoted as γ_(L1L2). The interfacialsurface energy between first liquid 300 and gas 306 is denoted asγ_(L1G). The interfacial surface energy between second liquid 302 andgas 306 is denoted as γ_(L2G). The interfacial surface energy betweenfirst liquid 300 and substrate 304 is denoted as γ_(SL1). Theinterfacial surface energy between second liquid 302 and substrate 304is denoted as γ_(SL2).

FIG. 3A depicts second liquid 302 as a drop disposed on first liquid300. Second liquid 302 does not deform first liquid 300 and does nottouch substrate 304. As depicted, first liquid 300 and second liquid 302do not intermix, and the interface between the first liquid and thesecond liquid is depicted as flat. At equilibrium, the contact angle ofsecond liquid 302 on first liquid 300 is θ, which is related to theinterfacial surface energies γ_(L1G), γ_(L2G), and γ_(L1L2) by Young'sequation:γ_(L1G)=γ_(L1L2)γ_(L2G)·cos(θ)  (1)Ifγ_(L1G)≥γ_(L1L2)+γ_(L2G)  (2)then θ=0°, and second liquid 302 spreads completely on first liquid 300.If the liquids are intermixable, then after some elapsed time,γ_(L1L2)=0  (3)In this case, the condition for complete spreading of second liquid 302on first liquid 300 isγ_(L1G)≥γ_(L2G)  (4)For thin films of first liquid 300 and small drops of second liquid 302,intermixing may be limited by diffusion processes. Thus, for secondliquid 302 to spread on first liquid 300, the inequality (2) is moreapplicable in the initial stages of spreading, when second liquid 302 isdisposed on first liquid 300 in the form of a drop.

FIG. 3B depicts contact angle formation for a drop of second liquid 302when the underlying layer of first liquid 300 is thick. In this case,the drop does not touch the substrate 304. Drop of second liquid 302 andlayer of first liquid 300 intersect at angles α, β, and θ, withα+β+θ=2π  (5)There are three conditions for the force balance along each interface:γ_(L2G)+γ_(L1L2)·cos(θ)+γ_(L1G)·cos(α)=0  (6)γ_(L2G)·cos(θ)+γ_(L1L2)+γ_(L1G)·cos(β)=0  (7)γ_(L2G)·cos(α)+γ_(L1L2)·cos(β)+γ_(L1G)=0  (8)If first liquid 300 and second liquid 302 are intermixable, thenγ_(L1L2)=0  (9)and equations (6)-(8) become:γ_(L2G)+γ_(L1G)·cos(α)=0  (10)γ_(L2G)·cos(θ)+γ_(L1G)·cos(β)=0  (11)γ_(L2G)·cos(α)+γ_(L1G)=0  (12)

Equations (10) and (12) givecos²(α)=1  (13)andα=0,π  (14)When second liquid 302 wets first liquid 300,α=π  (15)γ_(L2G)=γ_(L1G)  (16)and equation (11) givescos(θ)+cos(β)=0  (17)Combining this result with equations (5) and (15) gives:θ=0  (18)β=π  (19)Thus, equations (15), (18), and (19) give solutions for angles α, β, andθ.Whenγ_(L1G)≥γ_(L2G)  (20)there is no equilibrium between the interfaces. Equation (12) becomes aninequality even for α=π, and second liquid 302 spreads continuously onfirst liquid 300.

FIG. 3C depicts a more complex geometry for a drop of second liquid 302touching substrate 304 while also having an interface with first liquid300. Interfacial regions between first liquid 300, second liquid 302,and gas 306 (defined by angles α, β, and θ₁) and first liquid 300,second liquid 302, and substrate 304 (defined by angle θ₂) must beconsidered to determine spreading behavior of the second liquid on thefirst liquid.

The interfacial region between first liquid 300, second liquid 302, andgas 306 is governed by equations (6)-(8). Since first liquid 300 andsecond liquid 302 are intermixable,γ_(L1L2)=0  (21)The solutions for angle α are given by equation (14). In this case, letα=0  (22)andθ₁=π   (23)β=π  (24)Whenγ_(L1G)≥γ_(L2G)  (25)there is no equilibrium between the drop of second liquid 302 and firstliquid 300, and the drop spreads continuously along the interfacebetween the second liquid and the gas until limited by other physicallimitations (e.g., conservation of volume and intermixing).

For the interfacial region between first liquid 300, second liquid 302,and substrate 304, an equation similar to equation (1) should beconsidered:γ_(SL1)=γ_(SL2)+γ_(L1L2)·cos(θ₂)  (26)Ifγ_(SL1)≥γ_(SL2)+γ_(L1L2)  (27)the drop spreads completely, and θ₂=0.Again, as for the intermixable liquids, the second term γ_(L1L2)=0, andthe inequality (27) simplifies toγ_(SL1)≥γ_(SL2)  (28)The combined condition for the drop spreading is expressed asγ_(L1G)+γ_(SL1)≥γ_(L2G)+γ_(SL2)  (29)when energies before and after the spreading are considered. Thereshould be an energetically favorable transition (i.e., the transitionthat minimizes the energy of the system).

Different relationships between the four terms in the inequality (29)will determine the drop spreading character. The drop of second liquid302 can initially spread along the surface of the first liquid 300 ifthe inequality (25) is valid but the inequality (28) is not. Or the dropcan start spreading along liquid-solid interface provided the inequality(28) holds up and the inequality (25) does not. Eventually first liquid300 and second liquid 302 will intermix, thus introducing morecomplexity.

FIG. 3D depicts a geometry for a drop of second liquid 302 touchingsubstrate 304 while having an interface with first liquid 300. Asindicated in FIG. 3D, there are two interfacial regions of interest oneach side of the drop of second liquid 302. The first interfacial regionis where first liquid 300, second liquid 302, and gas 306 meet,indicated by angles α, β, and θ₁. The second interfacial region ofinterest is where first liquid 300, second liquid 302, and substrate 304meet, indicated by angle θ₂. Here, θ₁ approaches 0° and θ₂ approaches180° as the drop spreads when the surface tension of the interfacebetween second liquid 302 and substrate 304 exceeds the surface tensionof the interface between first liquid 300 and the substrate(γ_(SL2)≥γ_(SL1)). That is, drop of second liquid 302 spreads along theinterface between first liquid 300 and the second liquid and does notspread along the interface between the second liquid and substrate 304.

For the interface between first liquid 300, second liquid 302, and gas306, equations (6)-(8) are applicable. First liquid 300 and secondliquid 302 are intermixable, soγ_(L1L2)=0  (30)The solutions for angle α are given by equation (14). Forα=π  (31)Equation (11) givescos(θ₁)+cos(β)=0  (32)andθ₁=0  (33)β=π  (34)Whenγ_(L1G)≥γ_(L2G)  (35)there is no equilibrium between the drop of second liquid 302 and liquid300, and the drop spreads continuously along the interface between thesecond liquid and the gas until limited by other physical limitations(e.g., conservation of volume and intermixing).

For the interfacial region between second liquid 302 and substrate 304,

$\begin{matrix}{\gamma_{{SL}\; 1} = {\gamma_{{SL}\; 2} + {\gamma_{L\; 1L\; 2} \cdot {\cos\left( \theta_{2} \right)}}}} & (36) \\{{\cos\left( \theta_{2} \right)} = \frac{\gamma_{{SL}\; 1} - \gamma_{{SL}\; 2}}{\gamma_{L\; 1L\; 2}}} & (37)\end{matrix}$Ifγ_(SL1)≤γ_(SL2)  (38)and the liquids are intermixable, i.e.,γ_(L1L2)→0  (39)−∞≤cos(θ₂)≤−1  (40)the angle θ₂ approaches 180° and then becomes undefined. That is, secondliquid 302 has a tendency to contract along the substrate interface andspread along the interface between first liquid 300 and gas 306.

Spreading of second liquid 302 on first liquid 300 can be summarized forthree different cases, along with the surface energy relationship forcomplete spreading. In the first case, drop of second liquid 302 isdisposed on layer of first liquid 300, and the drop of the second liquiddoes not contact substrate 304. Layer of first liquid 300 can be thickor thin, and the first liquid 300 and second liquid 302 areintermixable. Under ideal conditions, when the surface energy of firstliquid 300 in the gas 306 is greater than or equal to the surface energyof the second liquid 302 in the gas (γ_(L1G)≥γ_(L2G)), completespreading of the drop of second liquid 302 occurs on layer of firstliquid 300. In the second case, drop of second liquid 302 is disposed onlayer of first liquid 300 while touching and spreading at the same timeon substrate 304. The first liquid and second liquid 302 areintermixable. Under ideal conditions, complete spreading occurs when:(i) the surface energy of first liquid 300 in the gas is greater than orequal to the surface energy of second liquid 302 in the gas(γ_(L1G)≥γ_(L2G)); and (ii) the surface energy of the interface betweenthe first liquid and substrate 304 exceeds the surface energy of theinterface between the second liquid and the substrate (γ_(SL1)≥γ_(SL2)).In the third case, drop of second liquid 302 is disposed on layer of thefirst liquid 300 while touching substrate 304. Spreading may occur alongthe interface between second liquid 302 and first liquid 300 or theinterface between the second liquid and substrate 304. The first liquidand second liquid 302 are intermixable. Under ideal conditions, completespreading occurs when the sum of the surface energy of first liquid 300in the gas and the surface energy of the interface between the firstliquid and substrate 304 is greater than or equal to the sum of thesurface energy of second liquid 302 in the gas and the surface energy ofthe interface between the second liquid and the substrate(γ_(L1G)+γ_(SL1)≥γ_(L2G)+γ_(SL2)) while the surface energy of firstliquid 300 in the gas is greater than or equal to the surface energy ofsecond liquid 302 in the gas (γ_(L1G)≥γ_(L2G)) or (ii) the surfaceenergy of the interface between the first liquid and substrate 304exceeds the surface energy of the interface between the second liquidand the substrate (γ_(SL1)≥γ_(SL2)).

By pretreating a nanoimprint lithography substrate with a liquidselected to have a surface energy greater than that of the imprintresist in the ambient atmosphere (e.g., air or an inert gas), the rateat which an imprint resist spreads on the substrate in a drop-on-demandnanoimprint lithography process may be increased and a more uniformthickness of the imprint resist on the substrate may be establishedbefore the imprint resist is contacted with the template, therebyfacilitating throughput in the nanoimprint lithography process. If thepretreatment composition includes polymerizable components capable ofintermixing with the imprint resist, then this can advantageouslycontribute to formation of the resulting polymeric layer without theaddition of undesired components, and may result in more uniform curing,thereby providing more uniform mechanical and etch properties.

FIG. 4 is a flowchart showing a process 400 for facilitating throughputin drop-on-demand nanoimprint lithography. Process 400 includesoperations 402-410. In operation 402, a pretreatment composition isdisposed on a nanoimprint lithography substrate to form a pretreatmentcoating on the substrate. In operation 404, discrete portions (“drops”)of an imprint resist are disposed on the pretreatment coating, with eachdrop covering a target area of the substrate. The pretreatmentcomposition and the imprint resist are selected such that theinterfacial surface energy between the pretreatment composition and theair exceeds the interfacial surface energy between the imprint resistand the air.

In operation 406, a composite polymerizable coating (“compositecoating”) is formed on the substrate as each drop of the imprint resistspreads beyond its target area. The composite coating includes ahomogeneous or inhomogeneous mixture of the pretreatment composition andthe imprint resist. In operation 408, the composite coating is contactedwith a nanoimprint lithography template (“template”), and allowed tospread and fill all the volume between the template and substrate. Inoperation 410, the composite coating is polymerized to yield a polymericlayer on the substrate. After polymerization of the composite coating,the template is separated from the polymeric layer, leaving ananoimprint lithography stack. As used herein, “nanoimprint lithographystack” generally refers to the substrate and the polymeric layer adheredto the substrate, each or both of which may include one or moreadditional (e.g., intervening) layers. In one example, the substrateincludes a base and an adhesion layer adhered to the base.

In process 400, the pretreatment composition and the imprint resist mayinclude a mixture of components as described, for example, in U.S. Pat.Nos. 7,157,036 and 8,076,386, as well as Chou et al. 1995, Imprint ofsub-25 nm vias and trenches in polymers, Applied Physics Letters67(21):3114-3116; Chou et al. 1996, Nanoimprint lithography, Journal ofVacuum Science Technology B 14(6): 4129-4133; and Long et al. 2007,Materials for step and flash imprint lithography (S-FIL®), Journal ofMaterials Chemistry 17:3575-3580, all of which are incorporated byreference herein. Suitable compositions include polymerizable monomers(“monomers”), crosslinkers, resins, photoinitiators, surfactants, or anycombination thereof. Classes of monomers include acrylates,methacrylates, vinyl ethers, and epoxides, as well as polyfunctionalderivatives thereof. In some cases, the pretreatment composition, theimprint resist, or both are substantially free of silicon. In othercases, the pretreatment composition, the imprint resist, or both aresilicon-containing. Silicon-containing monomers include, for example,siloxanes and disiloxanes. Resins can be silicon-containing (e.g.,silsesquioxanes) and non-silicon-containing (e.g., novolak resins). Thepretreatment composition, the imprint resist, or both may also includeone or more polymerization initiators or free radical generators.Classes of polymerization initiators include, for example,photoinitiators (e.g., acyloins, xanthones, and phenones), photoacidgenerators (e.g., sulfonates and onium salts), and photobase generators(e.g., ortho-nitrobenzyl carbamates, oxime urethanes, and O-acyloximes). In some cases, the pretreatment composition is free orsubstantially free of polymerization initiators, free radicalgenerators, or both.

Suitable monomers include monofunctional, difunctional, ormultifunctional acrylates, methacrylates, vinyl ethers, and epoxides, inwhich mono-, di-, and multi- refer to one, two, and three or more of theindicated functional groups, respectively. Some or all of the monomersmay be fluorinated (e.g., perfluorinated). In the case of acrylates, forexample, the pretreatment, the imprint resist, or both may include oneor more monofunctional acrylates, one or more difunctional acrylates,one or more multifunctional acrylates, or a combination thereof.

Examples of suitable monofunctional acrylates include isobornylacrylate, 3,3,5-trimethylcyclohexyl acrylate, dicyclopentenyl acrylate,benzyl acrylate, 1-naphthyl acrylate, 4-cyanobenzyl acrylate,pentafluorobenzyl acrylate, 2-phenylethyl acrylate, phenyl acrylate,(2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl acrylate, n-hexyl acrylate,4-tert-butylcyclohexyl acrylate, methoxy polyethylene glycol (350)monoacrylate, and methoxy polyethylene glycol (550) monoacrylate.

Examples of suitable diacrylates include ethylene glycol diacrylate,diethylene glycol diacrylate, triethylene glycol diacrylate,tetraethylene glycol diacrylate, polyethylene glycol diacrylate (e.g.,Mn, avg=575), 1,2-propanediol diacrylate, dipropylene glycol diacrylate,tripropylene glycol diacrylate, polypropylene glycol diacrylate,1,3-propanediol diacrylate, 1,4-butanediol diacrylate,2-butene-1,4-diacrylate, 1,3-butylene glycol diacrylate,3-methyl-1,3-butanediol diacrylate, 1,5-pentanediol diacrylate,1,6-hexanediol diacrylate, 1H,1H,6H,6H-perfluoro-1,6-hexanedioldiacrylate, 1,9-nonanediol diacrylate, 1,10-decanediol diacrylate,1,12-dodecanediol diacrylate, neopentyl glycol diacrylate, cyclohexanedimethanol diacrylate, tricyclodecane dimethanol diacrylate, bisphenol Adiacrylate, ethoxylated bisphenol A diacrylate, m-xylylene diacrylate,ethoxylated (3) bisphenol A diacrylate, ethoxylated (4) bisphenol Adiacrylate, ethoxylated (10) bisphenol A diacrylate, dicyclopentanyldiacrylate, 1,2-adamantanediol diacrylate, 2,4-diethylpentane-1,5-dioldiacrylate, poly(ethylene glycol) (400) diacrylate, poly(ethyleneglycol) (300) diacrylate, 1,6-hexanediol (EO)₂ diacrylate,1,6-hexanediol (EO)₅ diacrylate, and alkoxylated aliphatic diacrylateester.

Examples of suitable multifunctional acrylates includetrimethylolpropane triacrylate, propoxylated trimethylolpropanetriacrylate (e.g., propoxylated (3) trimethylolpropane triacrylate,propoxylated (6) trimethylolpropane triacrylate), trimethylolpropaneethoxylate triacrylate (e.g., n˜1.3, 3, 5), di(trimethylolpropane)tetraacrylate, propoxylated glyceryl triacrylate (e.g., propoxylated (3)glyceryl triacrylate), tris (2-hydroxy ethyl) isocyanurate triacrylate,pentaerythritol triacrylate, pentaerythritol tetracrylate, ethoxylatedpentaerythritol tetracrylate, dipentaerythritol pentaacrylate, andtripentaerythritol octaacrylate.

Examples of suitable crosslinkers include difunctional acrylates andmultifunctional acrylates, such as those described herein.

Examples of suitable photoinitiators include IRGACURE 907, IRGACURE4265, 651, 1173, 819, TPO, and TPO-L.

A surfactant can be applied to a patterned surface of an imprintlithography template, added to an imprint lithography resist, or both,to reduce the separation force between the solidified resist and thetemplate, thereby reducing separation defects in imprinted patternsformed in an imprint lithography process and to increase the number ofsuccessive imprints that can be made with an imprint lithographytemplate. Factors in selecting a surfactant for an imprint resistinclude, for example, affinity with the surface and desired surfaceproperties of the treated surface.

Examples of suitable surfactants include fluorinated and non-fluorinatedsurfactants. The fluorinated and non-fluorinated surfactants may beionic or non-ionic surfactants. Suitable non-ionic fluorinatedsurfactants include fluoro-aliphatic polymeric esters, perfluoroethersurfactants, fluorosurfactants of polyoxyethylene, fluorosurfactants ofpolyalkyl ethers, fluoroalkyl polyethers, and the like. Suitablenon-ionic non-fluorinated surfactants include ethoxylated alcohols,ethoxylated alkylphenols, and polyethyleneoxide-polypropyleneoxide blockcopolymers.

Exemplary commercially available surfactant components include, but arenot limited to, ZONYL® FSO and ZONYL® FS-300, manufactured by E.I. duPont de Nemours and Company having an office located in Wilmington,Del.; FC-4432 and FC-4430, manufactured by 3M having an office locatedin Maplewood, Minn.; MASURF® FS-1700, FS-2000, and FS-2800 manufacturedby Pilot Chemical Company having an office located in Cincinnati, Ohio.;S-107B, manufactured by Chemguard having an office located in Mansfield,Tex.; FTERGENT 222F, FTERGENT 250, FTERGENT 251, manufactured by NEOSChemical Chuo-ku, Kobe-shi, Japan; PolyFox PF-656, manufactured byOMNOVA Solutions Inc. having an office located in Akron, Ohio; PluronicL35, L42, L43, L44, L63, L64, etc. manufactured by BASF having an officelocated in Florham Park, N.J.; and Brij 35, 58, 78, etc. manufactured byCroda Inc. having an office located in Edison, N.J.

In some examples, an imprint resist includes 0 wt % to 80 wt % (e.g., 20wt % to 80 wt % or 40 wt % to 80 wt %) of one or more monofunctionalacrylates; 90 wt % to 98 wt % of one or more difunctional ormultifunctional acrylates (e.g., the imprint resist may be substantiallyfree of monofunctional acrylates) or 20 wt % to 75 wt % of one or moredifunctional or multifunctional acrylates (e.g., when one or moremonofunctional acrylates is present); 1 wt % to 10 wt % of one or morephotoinitiators; and 1 wt % to 10 wt % of one or more surfactants. Inone example, an imprint resist includes about 40 wt % to about 50 wt %of one or more monofunctional acrylates, about 45 wt % to about 55 wt %of one or more difunctional acrylates, about 4 wt % to about 6 wt % ofone or more photoinitiators, and about 3 wt % surfactant. In anotherexample, an imprint resist includes about 44 wt % of one or moremonofunctional acrylates, about 48 wt % of one or more difunctionalacrylates, about 5 wt % of one or more photoinitiators, and about 3 wt %surfactant. In yet another example, an imprint resist includes about 10wt % of a first monofunctional acrylate (e.g., isobornyl acrylate),about 34 wt % of a second monofunctional acrylate (e.g., benzylacrylate) about 48 wt % of a difunctional acrylate (e.g., neopentylglycol diacrylate), about 2 wt % of a first photoinitiator (e.g.,IRGACURE TPO), about 3 wt % of a second photoinitiator (e.g., DAROCUR4265), and about 3 wt % surfactant. Examples of suitable surfactantsinclude X—R—(OCH₂CH₂)_(n)OH, where R=alkyl, aryl, or poly(propyleneglycol), X═H or —(OCH₂CH₂)_(n)OH, and n is an integer (e.g., 2 to 20, 5to 15, or 10 to 12) (e.g., X═—(OCH₂CH₂)_(n)OH, R=poly(propylene glycol),and n=10 to 12); Y—R—(OCH₂CH₂)_(n)OH, where R=alkyl, aryl, orpoly(propylene glycol), Y=a fluorinated moiety (e.g., perfluorinatedalkyl or perfluorinated ether) or poly(ethylene glycol) capped with afluorinated moiety, and n is an integer (e.g., 2 to 20, 5 to 15, or 10to 12) (e.g., Y=poly(ethylene glycol) capped with a perfluorinated alkylgroup, R=poly(propylene glycol), and n=10 to 12); and a combinationthereof. The viscosity of the imprint resist is typically between 0.1 cPand 25 cP, or between 5 cP and 15 cP at 23° C. The interfacial surfaceenergy between the imprint resist and air is typically between 20 mN/mand 36 mN/m.

In one example, a pretreatment composition includes 0 wt % to 80 wt %(e.g., 20 wt % to 80 wt % or 40 wt % to 80 wt %) of one or moremonofunctional acrylates; 90 wt % to 100 wt % of one or moredifunctional or multifunctional acrylates (e.g., the pretreatmentcomposition is substantially free of monofunctional acrylates) or 20 wt% to 75 wt % of one or more difunctional or multifunctional acrylates(e.g., when one or more monofunctional acrylates is present); and 0 wt %to 10 wt % of one or more photoinitiators; and 0 wt % to 10 wt % of oneor more surfactants.

The pretreatment composition is typically miscible with the imprintresist. The pretreatment composition typically has a low vapor pressure,such that it remains present as a thin film on the substrate until thecomposite coating is polymerized. In one example, the vapor pressure ofa pretreatment composition is less than 1×10⁻⁴ mmHg at 25° C. Thepretreatment composition also typically has a low viscosity tofacilitate rapid spreading of the pretreatment composition on thesubstrate. In one example, the viscosity of a pretreatment compositionis less than 90 cP at 25° C. The interfacial surface energy between thepretreatment composition and air is typically between 30 mN/m and 45mN/m. The pretreatment composition is typically selected to bechemically stable, such that decomposition does not occur during use.

A pretreatment composition may be a single polymerizable component(e.g., a monomer such as a monofunctional acrylate, a difunctionalacrylate, or a multifunctional acrylate), a mixture of two or morepolymerizable components (e.g., a mixture of two or more monomers), or amixture of one or more polymerizable components and one or more othercomponents (e.g., a mixture of monomers; a mixture of two or moremonomers and a surfactant, a photoinitiator, or both; and the like). Insome examples, a pretreatment composition includes trimethylolpropanetriacrylate, trimethylolpropane ethoxylate triacrylate,1,12-dodecanediol diacrylate, poly(ethylene glycol) diacrylate,tetraethylene glycol diacrylate, 1,3-adamantanediol diacrylate,nonanediol diacrylate, m-xylylene diacrylate, tricyclodecane dimethanoldiacrylate, or any combination thereof.

Mixtures of polymerizable components may result in synergistic effects,yielding pretreatment compositions having a more advantageouscombination of properties (e.g., low viscosity, good etch resistance,and film stability) than a pretreatment composition with a singlepolymerizable component. In one example, the pretreatment composition isa mixture of 1,12-dodecanediol diacrylate and tricyclodecane dimethanoldiacrylate. In another example, the pretreatment composition is amixture of tricyclodecane dimethanol diacrylate and tetraethylene glycoldiacrylate. The pretreatment composition is generally selected such thatone or more components of the pretreatment composition polymerizes(e.g., covalently bonds) with one or more components of the imprintresist during polymerization of the composite polymerizable coating. Insome cases, the pretreatment composition includes a polymerizablecomponent that is also in the imprint resist, or a polymerizablecomponent that has a functional group in common with one or morepolymerizable components in the imprint resist (e.g., an acrylategroup). Suitable examples of pretreatment compositions includemultifunctional acrylates such as those described herein, includingpropoxylated (3) trimethylolpropane triacrylate, trimethylolpropanetriacrylate, and dipentaerythritol pentaacrylate.

A pretreatment composition may be selected such that the etch resistanceis generally comparable to the etch resistance of the imprint resist,thereby promoting etch uniformity. In certain cases, a pretreatmentcomposition is selected such that the interfacial surface energy at aninterface between the pretreatment and air exceeds that of the imprintresist used in conjunction with the pretreatment composition, therebypromoting rapid spreading of the liquid imprint resist on the liquidpretreatment composition to form a uniform composite coating on thesubstrate before the composite coating is contacted with the template.The interfacial surface energy between the pretreatment composition andair typically exceeds that between the imprint resist and air or betweenat least a component of the imprint resist and air by 1 mN/m to 25 mN/m,1 mN/m to 15 mN/m, or 1 mN/m to 7 mN/m, although these ranges may varybased on chemical and physical properties of the pretreatmentcomposition and the imprint resist and the resulting interaction betweenthese two liquids. When the difference between surface energies is toolow, limited spreading of the imprint resist results, and the dropsmaintain a spherical cap-like shape and remain separated by thepretreatment composition. When the difference between surface energiesis too high, excessive spreading of the imprint resist results, withmost of the imprint resist moving toward the adjacent drops, emptyingthe drop centers, such that the composite coating has convex regionsabove the drop centers. Thus, when the difference between surfaceenergies is too low or too high, the resulting composite coating isnonuniform, with significant concave or convex regions. When thedifference in surface energies is appropriately selected, the imprintresist spreads quickly to yield a substantially uniform compositecoating. Advantageous selection of the pretreatment composition and theimprint resist allows fill time to be reduced by 50-90%, such thatfilling can be achieved in as little as 1 sec, or in some cases even aslittle as 0.1 sec.

Referring to operation 402 of process 400, FIG. 5A depicts substrate 102including base 500 and adhesion layer 502. Base 500 is typically asilicon wafer. Other suitable materials for base 500 include fusedsilica, quartz, silicon germanium, gallium arsenide, and indiumphosphide. Adhesion layer 502 serves to increase adhesion of thepolymeric layer to base 500, thereby reducing formation of defects inthe polymeric layer during separation of the template from the polymericlayer after polymerization of the composite coating. A thickness ofadhesion layer 502 is typically between 1 nm and 10 nm. Examples ofsuitable materials for adhesion layer 502 include those disclosed inU.S. Pat. Nos. 7,759,407; 8,361,546; 8,557,351; 8,808,808; and8,846,195, all of which are incorporated by reference herein. In oneexample, an adhesion layer is formed from a composition including ISORAD501, CYMEL 303ULF, CYCAT 4040 or TAG 2678 (a quaternary ammonium blockedtrifluoromethanesulfonic acid), and PM Acetate (a solvent consisting of2-(1-methoxy)propyl acetate available from Eastman Chemical Company ofKingsport, Tenn.). In some cases, substrate 102 includes one or moreadditional layers between base 500 and adhesion layer 502. In certaincases, substrate 102 includes one or more additional layers on adhesionlayer 502. For simplicity, substrate 102 is depicted as including onlybase 500 and adhesion layer 502.

FIG. 5B depicts pretreatment composition 504 after the pretreatmentcomposition has been disposed on substrate 102 to form pretreatmentcoating 506. As depicted in FIG. 5B, pretreatment coating 506 is formeddirectly on adhesion layer 502 of substrate 102. In some cases,pretreatment coating 506 is formed on another surface of substrate 102(e.g., directly on base 500). Pretreatment coating 506 is formed onsubstrate 102 using techniques such as spin-coating, dip coating,chemical vapor deposition (CVD), physical vapor deposition (PVD). In thecase of, for example, spin-coating or dip coating and the like, thepretreatment composition can be dissolved in one or more solvents (e.g.,propylene glycol methyl ether acetate (PGMEA), propylene glycolmonomethyl ether (PGME), and the like) for application to the substrate,with the solvent then evaporated away to leave the pretreatment coating.A thickness t_(p) of pretreatment coating 506 is typically between 1 nmand 100 nm (e.g., between 1 nm and 50 nm, between 1 nm and 25 nm, orbetween 1 nm and 10 nm).

Referring again to FIG. 4, operation 404 of process 400 includesdisposing drops of imprint resist on the pretreatment coating, such thateach drop of the imprint resist covers a target area of the substrate. Avolume of the imprint resist drops is typically between 0.6 pL and 30pL, and a distance between drop centers is typically between 35 μm and350 μm. In some cases, the volume ratio of the imprint resist to thepretreatment is between 1:1 and 15:1. In operation 406, a compositecoating is formed on the substrate as each drop of the imprint resistspreads beyond its target area, forming a composite coating. As usedherein, “prespreading” refers to the spontaneous spreading of the dropsof imprint resist that occurs between the time when the drops initiallycontact the pretreatment coating and spread beyond the target areas, andthe time when the template contacts the composite coating.

FIGS. 6A-6D depict top-down views of drops of imprint resist onpretreatment coating at the time of disposal of the drops on targetareas, and of the composite coating before, during, and at the end ofdrop spreading. Although the drops are depicted in a square grid, thedrop pattern is not limited to square or geometric patterns.

FIG. 6A depicts a top-down view of drops 600 on pretreatment coating 506at the time when the drops are initially disposed on the pretreatmentcoating, such that the drops cover but do not extend beyond target areas602. After drops 600 are disposed on pretreatment coating 506, the dropsspread spontaneously to cover a surface area of the substrate largerthan that of the target areas, thereby forming a composite coating onthe substrate. FIG. 6B depicts a top-down view of composite coating 604during prespreading (after some spreading of drops 600 beyond the targetareas 602), and typically after some intermixing of the imprint resistand the pretreatment. As depicted, composite coating 604 is a mixture ofthe liquid pretreatment composition and the liquid imprint resist, withregions 606 containing a majority of imprint resist (“enriched” withimprint resist), and regions 608 containing a majority of pretreatment(“enriched” with pretreatment). As prespreading progresses, compositecoating 604 may form a more homogeneous mixture of the pretreatmentcomposition and the imprint resist.

Spreading may progress until one or more of regions 606 contacts one ormore adjacent regions 606. FIGS. 6C and 6D depict composite coating 604at the end of spreading. As depicted in FIG. 6C, each of regions 606 hasspread to contact each adjacent region 606 at boundaries 610, withregions 608 reduced to discrete (non-continuous) portions betweenregions 606. In other cases, as depicted in FIG. 6D, regions 606 spreadto form a continuous layer, such that regions 608 are notdistinguishable. In FIG. 6D, composite coating 604 may be a homogenousmixture of the pretreatment composition and the imprint resist.

FIGS. 7A-7D are cross-sectional views along lines w-w, x-x, y-y, and z-zof FIGS. 6A-D, respectively. FIG. 7A is a cross-sectional view alongline w-w of FIG. 6A, depicting drops of imprint resist 600 covering asurface area of substrate 102 corresponding to target areas 602. Eachtarget area (and each drop as initially disposed) has a center asindicated by line c-c, and line b-b indicates a location equidistantbetween the centers of two target areas 602. For simplicity, drops 600are depicted as contacting adhesion layer 502 of substrate 102, and nointermixing of the imprint resist and the pretreatment composition isdepicted. FIG. 7B is a cross-sectional view along line x-x of FIG. 6B,depicting composite coating 604 with regions 608 exposed between regions606, after regions 606 have spread beyond target areas 602. FIG. 7C is across-sectional view along line y-y of FIG. 6C at the end ofprespreading, depicting composite coating 604 as a homogeneous mixtureof the pretreatment composition and imprint resist. As depicted, regions606 have spread to cover a greater surface of the substrate than in FIG.7B, and regions 608 are correspondingly reduced. Regions 606 originatingfrom drops 600 are depicted as convex, however, composite coating 604may be substantially planar or include concave regions. In certaincases, prespreading may continue beyond that depicted in FIG. 7C, withthe imprint resist forming a continuous layer over the pretreatment(with no intermixing or with full or partial intermixing). FIG. 7D is across-sectional view along line z-z of FIG. 6D, depicting compositecoating 604 as a homogenous mixture of the pretreatment composition andthe imprint resist at the end of spreading, with concave regions of thecomposite coating about drop centers cc meeting at boundaries 610, suchthat the thickness of the polymerizable coating at the drop boundariesexceeds the thickness of the composite coating of the drop centers. Asdepicted in FIGS. 7C and 7D, a thickness of composite coating 604 at alocation equidistant between the centers of two target areas may differfrom a thickness of the composite coating at the center of one of thetwo target areas when the composite coating is contacted with thenanoimprint lithography template.

Referring again to FIG. 4, operations 408 and 410 of process 400 includecontacting the composite coating with a template, and polymerizing thecomposite coating to yield a nanoimprint lithography stack having acomposite polymeric layer on the nanoimprint lithography substrate,respectively.

In some cases, as depicted in FIGS. 7C and 7D, composite coating 604 isa homogeneous mixture or substantially homogenous mixture (e.g., at theair-composite coating interface) at the end of prespreading (i.e., justbefore the composite coating is contacted with the template). As such,the template contacts a homogenous mixture, with a majority of themixture typically derived from the imprint resist. Thus, the releaseproperties of the imprint resist would generally govern the interactionof the composite coating with the template, as well as the separation ofthe polymeric layer from the template, including defect formation (orabsence thereof) due to separation forces between the template and thepolymeric layer.

As depicted in FIGS. 8A and 8B, however, composite coating 604 mayinclude regions 608 and 606 that are enriched with the pretreatmentcomposition and enriched with the imprint resist, respectively, suchthat template 110 contacts regions of composite coating 604 havingdifferent physical and chemical properties. For simplicity, the imprintresist in regions 606 is depicted as having displaced the pretreatmentcoating, such that regions 606 are in direct contact with the substrate,and no intermixing is shown. Thus, the pretreatment composition inregions 608 is non-uniform in thickness. In FIG. 8A, the maximum heightp of regions 606 exceeds the maximum height i of the pretreatmentcomposition, such that template 110 primarily contacts regions 606. InFIG. 8B maximum height i of regions 608 exceeds the maximum height p ofthe imprint resist, such that template 110 primarily contacts regions608. Thus, separation of template 110 from the resulting compositepolymeric layer and the defect density associated therewith isnonuniform and based on the different interactions between the templateand the imprint resist and between the template and the pretreatmentcomposition. Thus, for certain pretreatment compositions (e.g.,pretreatment compositions that include a single monomer or a mixture oftwo or more monomers, but no surfactant), it may be advantageous for thecomposite coating to form a homogenous mixture, or at least asubstantially homogenous mixture at the gas-liquid interface at whichthe template contacts the composite coating.

FIGS. 9A-9C and 10A-10C are cross-sectional views depicting template 110and composite coating 604 on substrate 102 having base 500 and adhesionlayer 502 before and during contact of the composite coating with thetemplate, and after separation of the template from the compositepolymeric layer to yield a nanoimprint lithography stack. In FIGS.9A-9C, composite coating 604 is depicted as a homogeneous mixture of thepretreatment composition and the imprint resist. In FIGS. 10A-10C,composite coating 604 is depicted as an inhomogeneous mixture of thepretreatment composition and the imprint resist.

FIG. 9A depicts a cross-sectional view of initial contact of template110 with homogeneous composite coating 900 on substrate 102. In FIG. 9B,template 110 has been advanced toward substrate 102 such that compositecoating 900 fills recesses of template 110. After polymerization ofcomposite coating 900 to yield a homogeneous polymeric layer onsubstrate 102, template 110 is separated from the polymeric layer. FIG.9C depicts a cross-sectional view of nanoimprint lithography stack 902having homogeneous composite polymeric layer 904.

FIG. 10A depicts a cross-sectional view of initial contact of template110 with composite coating 604 on substrate 102. Inhomogeneous compositecoating 1000 includes regions 606 and 608. As depicted, little or nointermixing has occurred between the imprint resist in region 606 andthe pretreatment composition in region 608. In FIG. 10B, template 110has been advanced toward substrate 102 such that composite coating 1000fills recesses of template 110. After polymerization of compositecoating 1000 to yield an inhomogeneous polymeric layer on substrate 102,template 110 is separated from the polymeric layer. FIG. 10C depicts across-sectional view of nanoimprint lithography stack 1002 havinginhomogeneous polymeric layer 1004 with regions 1006 and 1008corresponding to regions 606 and 608 of inhomogeneous composite coating1000. Thus, the chemical composition of composite polymeric layer 1002is inhomogeneous or non-uniform, and includes regions 1006 having acomposition derived from a mixture enriched with the imprint resist andregions 1008 having a composition derived from a mixture enriched withthe pretreatment composition. The relative size (e.g., exposed surfacearea, surface area of template covered, or volume) of regions 1006 and1008 may vary based at least in part on the extent of prespreadingbefore contact of the composite coating with the template or spreadingdue to contact with the template. In some cases, regions 1006 may beseparated or bounded by regions 1008, such that composite polymericlayer 1002 includes a plurality of center regions separated byboundaries, with the chemical composition of the composite polymericlayer 1004 at the boundaries differing from the chemical composition ofthe composite polymeric layer at the interior of the center regions.

In some cases, after polymerization of a composite coating in an imprintlithography process, a portion of the pretreatment composition mayremain uncured (e.g., pretreatment composition beyond the boundaries ofan imprinted field). The presence of uncured pretreatment coating may bedisadvantageous for a variety of reasons. In one example, uncuredpretreatment coating may cause defects in an imprint lithography processif pretreatment composition is allowed to spread onto a compositedpolymeric layer (an imprinted field). In another example, evaporation ofuncured pretreatment coating may contaminate portions of the nanoimprintlithography substrate or portions of the equipment in which theimprinting is performed. By including a polymerization initiator in thepretreatment composition that is activated independently from thepolymerization initiator in the imprint resist, uncured pretreatmentcoating may be polymerized (e.g., in unimprinted areas of a nanoimprintlithography substrate) after a composite polymerizable layer ispolymerized to yield the composite polymeric layer, thereby avoidingdisadvantages associated with the presence of uncured pretreatmentcoating after polymerization of a composite polymerizable coating.Independent activation of the polymerization initiator in a pretreatmentcomposition may be achieved by including a thermal initiator or aphotoinitiator that is activated at a different wavelength, intensity,energy density, duration, or combination thereof than the photoinitiatorin the imprint resist, such that an uncured portion of the pretreatmentcoating present after polymerization of the composite polymerizablecoating may be polymerized in a separate process, such as heating orirradiating at a wavelength, intensity, energy density, duration, orcombination thereof other than that used to initiate polymerization ofthe composite polymerizable coating. As used herein, “wavelength”generally refers to a portion of the electromagnetic spectrum (e.g., asingle wavelength or a wavelength range).

As described herein, application of a pretreatment composition to asubstrate typically includes covering a surface of the substrate that isto be imprinted via a spin-coating process to yield an uncuredpretreatment coating on the substrate. As such, any area of thesubstrate that is not subsequently covered with imprint resist mayremain covered with uncured pretreatment coating after polymerization ofthe composite polymerizable coating. As depicted in FIG. 11 with respectto nanoimprint lithography substrate 1100, uncured pretreatment coating1102 may be found in the relatively small gaps (the “street”) betweenadjacent imprints 1104 or in the relatively larger unimprinted areas1106 at the edge of the substrate (e.g., partial fields with an areabelow some minimum value). Uncured pretreatment coating may beproblematic, for example, if it spreads or evaporates at a later time.In one example, uncured pretreatment coating may spread onto imprintedareas 1104 of substrate 1100, causing defects such as line collapse. Inanother example, uncured pretreatment coating may evaporate duringstorage or during subsequent process steps. Evaporation during storagemay result in contamination of storage containers, other substrates, orboth. During subsequent process steps, any pretreatment coating thatevaporates or spreads may contaminate substrate handling equipment orprocess environments. The presence of evaporated pretreatment coating ina process chamber may negatively impact a subsequent process step, suchas an etch step or a deposition process, by altering etch rate, layeruniformity, or both.

Including a polymerization initiator in a pretreatment composition thatis activated independently of the polymerization initiator in an imprintresist ensures that the pretreatment coating is not unintentionallycured in areas that will undergo subsequent imprinting. For example,during polymerization of a composite polymerizable coating formed withan imprint resist that includes a photoinitiator, it may be difficult toprevent stray UV radiation from reaching areas beyond the imprint field.If such stray UV radiation initiates polymerization of pretreatmentcoating in a portion of an adjacent field, and an imprint resist issubsequently disposed on the cured or partially cured pretreatmentcomposition, the cured or partially cured pretreatment composition mayreduce the spreading of the imprint resist, resulting in lowerthroughput, increased defectivity, or both.

FIG. 12A is a flowchart showing process 1200 to achieve independent or“orthogonal” polymerization of an uncured portion of a pretreatmentcoating by including a photoinitiator in the imprint resist andincluding, in the pretreatment composition, a thermal initiator that isnot sensitive to the UV radiation used to initiate the photoinitiator inthe imprint resist. In 1202, a composite polymerizable coating isirradiated with UV radiation to initiate polymerization of the compositepolymerizable coating via a photoinitiator in the imprint resist toyield composite polymeric layer and an uncured portion of thepretreatment coating. In 1204, after some or all of the substrate hasbeen imprinted, the uncured portion of the pretreatment coating isheated to a temperature and for a duration sufficient to polymerize theuncured portion of the pretreatment coating via the thermal initiator.The temperature required to polymerize the uncured portion of thepretreatment coating is typically below the glass transition temperatureof the imprint resist, such that the composite polymeric layer is notdamaged by conditions required for polymerization of the uncured portionof the pretreatment coating. While some thermal initiators may also besensitive to UV irradiation, the wavelengths used to cure thephotoinitiator may be selected to avoid reaction of the thermalinitiator in the pretreatment composition in response to the UVirradiation.

Suitable thermal initiators include azo compounds and organic peroxides.Examples of suitable azo compounds for thermal free radical initiationinclude 2,2′-azobisisobutyronitrile (AIBN) and1,1′-azobis(cyclohexanecarbonitrile). Examples of suitable organicperoxides include benzoyl peroxide, dicumyl peroxide, di-tert-butylperoxide, tert-butyl peroxybenzoate. tert-amyl peroxybenzoate, lauroylperoxide, 1,1-bis(tert-butylperoxy)cyclohexane,2,5-bis(tert-butylperoxy)-2,5-dimethylhexane,bis[1-(tert-butylperoxy)-1-methylethyl]benzene, and1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane.

FIG. 12B is a flowchart showing process 1210 to achieve independent ororthogonal polymerization of an uncured portion of a pretreatmentcoating by including a first photoinitiator in the imprint resist and asecond photoinitiator in the pretreatment composition. In some cases,the first photoinitiator and the second photoinitiator are the same(i.e., have the same chemical structure). When the first and secondphotoinitiators are the same, the concentration of the first and secondphotoinitiators may be the same or different. Independent or orthogonalpolymerization of the uncured portion of the pretreatment coating andthe imprint resist when the first and second photoinitiators are thesame may be achieved via spatial control of UV radiation, differences inintensity, energy density, or duration of UV radiation, or a combinationthereof. In certain cases, the first photoinitiator and the secondphotoinitiator are different (i.e., have a different chemicalstructure). When the first and second photoinitiators are different, theconcentration of the first and second photoinitiators may be the same ordifferent. Independent or orthogonal polymerization of the uncuredportion of the pretreatment coating and the imprint resist when thefirst and second photoinitiators are different may also be achieved viaspatial control of UV radiation, differences in intensity, energydensity, duration of UV radiation, or a combination thereof.

In 1212, a composite polymerizable coating is irradiated with UVradiation at a first wavelength, first intensity, first energy density,duration, or combination thereof to initiate polymerization of thecomposite polymerizable coating via the first photoinitiator to yield acomposite polymeric layer and an uncured portion of the pretreatmentcoating. In 1214, after some or all of the substrate has been imprinted,the uncured portion of the pretreatment coating is irradiated with UVradiation at a second activation wavelength, second intensity, secondenergy density, duration, or combination thereof to polymerize theuncured portion of the pretreatment coating via the secondphotoinitiator. In some cases, activation of the second photoinitiatormay require at least one of a shorter wavelength, higher intensity,higher energy density, and longer duration than the firstphotoinitiator.

In one example of process 1210, the imprint resist includes a firstphotoinitiator and the pretreatment composition include a secondphotoinitiator. The first photoinitiator has a lower energy (longerwavelength) threshold than the second photoinitiator. Irradiating thecomposite polymerizable coating at the longer wavelength yields acomposite polymeric layer and an uncured portion of the pretreatmentcoating (i.e., stray UV radiation from the polymerization of thecomposite polymerizable coating does not initiate polymerization ofpretreatment coating that has not formed part of the compositepolymerizable coating). After some or all of a substrate has beenimprinted, the uncured portion of the pretreatment coating ispolymerized by exposing the uncured portion of the pretreatment coatingto shorter wavelength UV radiation, thereby curing the uncured portionof the pretreatment coating independently of the composite polymerizablecoating.

Examples of suitable photoinitiators include alpha-hydroxyketone typephotoinitiators, such as Irgacure 184, 2959, 127, and Darocur 1173;alpha-aminoketone type photoinitiators, such as Irgacure 369 and 907;phenylglyoxylate type photoinitiators, such as Irgacure 754 and DarocurMBF; benzyldimethyl-ketal type photoinitiators, such as Irgacure 651;monoacylphosphine oxide (MAPO) type photoinitiators, such as Lucirin TPOand Lucirin TPO-L; and bisacylphosphine oxide (BAPO) typephotoinitiators, such as Irgacure 819.

An example of a suitable pair of initiators to achieve independent ororthogonal polymerization include Irgacure 819 with Irgacure 184.Irgacure 819, a bisacylphospine oxide (BAPO) type photoinitiator, can beactivated at relatively lower energy (longer wavelength) than Irgacure184, an alpha-hydroxyketone type photoinitiator. Irgacure 819 may beused in the imprint resist to activate polymerization of the compositepolymerizable coating, and Irgacure 184 may be used in the pretreatmentcomposition to polymerize any uncured material after the imprintingprocess has been completed on the substrate. In one example, thecomposite polymerizable composition is cured at wavelengths greater thanabout 380 nm and uncured pretreatment coating is cured after imprintingat wavelengths less than about 360 nm (e.g., at absorption maxima atabout 246, 280 and/or 333 nm).

In another example of process 1210, the imprint resist includes a firstphotoinitiator and the pretreatment composition includes a second, lesssensitive photoinitiator, such that the UV radiation of a firstwavelength, first intensity, first energy density, first duration, orcombination thereof sufficient to initiate polymerization of thecomposite polymerizable coating is insufficient to polymerize theuncured portion of the pretreatment coating. After some or all of thesubstrate has been imprinted, the uncured portion of the pretreatmentcoating is polymerized by exposing the uncured portion of thepretreatment coating to UV radiation of the first wavelength and asecond intensity, second energy density, second duration, or combinationthereof, where at least one of the second intensity, energy density, andduration exceeds at least one of the first intensity, energy density,and duration and is sufficient to polymerize the uncured portion of thepretreatment coating via the second photoinitiator without damaging thecomposite polymeric layer.

In yet another example of process 1210, the imprint resist and thepretreatment composition include the same photoinitiator, and theimprint resist, but not the pretreatment composition, includes aphotosensitizer to enhance the sensitivity of the photoinitiator in thecomposite polymerizable coating relative to that of the pretreatmentcomposition. UV radiation of a first wavelength and first intensity orfirst energy density to initiate polymerization of the compositepolymerizable coating is insufficient to polymerize the uncured portionof the pretreatment coating. After some or all of the substrate has beenimprinted, the uncured portion of the pretreatment coating ispolymerized by exposing the uncured portion of the pretreatment coatingto UV radiation of the first wavelength and a second intensity or energydensity, wherein the second intensity or energy density exceeds thefirst intensity or energy density and is sufficient to initiatepolymerization of the uncured portion of the pretreatment coating.

Examples of suitable photosensitizers include4,4′-bis(diethylamino)benzophenone, 2-isopropylthioxanthone,benzophenone, phenyl benzophenone, 4-benzoyl-4′-methyldiphenyl sulfide,methyl 2-benzoylbenzoate, xanthone, t-butyl anthraquinone,phenothiazine, and 7-diethylamino-4-methylcoumarin. Examples of suitablephotoinitiators are described herein for use with imprint resists.

FIG. 12C is a flowchart showing process 1220 to achieve independent ororthogonal polymerization of a pretreatment composition by inducingautopolymerization of a pretreatment composition free of polymerizationinitiator via irradiation having a high intensity, high energy density,or combination thereof. The imprint resist includes a firstphotoinitiator, and the pretreatment composition is free ofpolymerization initiator. In 1222, the composite polymerizable coatingis irradiated with UV radiation at a first wavelength, first intensity,first energy density, first duration, or combination thereof to initiatepolymerization of the composite polymerizable coating via the firstphotoinitiator to yield a composite polymeric layer and an uncuredportion of the pretreatment coating. In 1224, after some or all of thesubstrate has been imprinted, the uncured portion of the pretreatmentcoating is irradiated with UV radiation at the first wavelength or adifferent wavelength and a second intensity, energy density, duration,or combination thereof to autopolymerize the uncured portion of thepretreatment coating. In one example, to achieve autopolymerization ofthe pretreatment composition, the uncured portion of the pretreatmentcoating is exposed to UV radiation at the first wavelength and a secondintensity, energy density, or duration exceeding the first intensity,energy density, or duration to polymerize the uncured portion ofpretreatment coating. Quenching of the autopolymerization may be avoidedby excluding oxygen from the environment in which the uncured portion ofthe pretreatment coating is polymerized.

EXAMPLES

In the Examples below, the reported interfacial surface energy at theinterface between the imprint resist and air was measured by the maximumbubble pressure method. The measurements were made using a BP2 bubblepressure tensiometer manufactured by Krüss GmbH of Hamburg, Germany. Inthe maximum bubble pressure method, the maximum internal pressure of agas bubble which is formed in a liquid by means of a capillary ismeasured. With a capillary of known diameter, the surface tension can becalculated from the Young-Laplace equation. For the some of thepretreatment compositions, the manufacturer's reported values for theinterfacial surface energy at the interface between the pretreatmentcomposition and air are provided.

The viscosities were measured using a Brookfield DV-II+ Pro with a smallsample adapter using a temperature-controlled bath set at 23° C.Reported viscosity values are the average of five measurements.

Adhesion layers were prepared on substrates formed by curing an adhesivecomposition made by combining about 77 g ISORAD 501, about 22 g CYMEL303ULF, and about 1 g TAG 2678, introducing this mixture intoapproximately 1900 grams of PM Acetate. The adhesive composition wasspun onto a substrate (e.g., a silicon wafer) at a rotational velocitybetween 500 and 4,000 revolutions per minute so as to provide asubstantially smooth, if not planar layer with uniform thickness. Thespun-on composition was exposed to thermal actinic energy of 160° C. forapproximately two minutes. The resulting adhesion layers were about 3 nmto about 4 nm thick.

In Comparative Example 1 and Examples 1-3, an imprint resist with asurface tension of 33 mN/m at an air/imprint resist interface was usedto demonstrate spreading of the imprint resist on various surfaces. Theimprint resist was a polymerizable composition including about 45 wt %monofunctional acrylate (e.g., isobornyl acrylate and benzyl acrylate),about 48 wt % difunctional acrylate (e.g., neopentyl glycol diacrylate),about 5 wt % photoinitiator (e.g., TPO and 4265), and about 3 wt %surfactant (e.g., a mixture of X—R—(OCH₂CH₂)_(n)OH, where R=alkyl, aryl,or poly(propylene glycol), X═H or —(OCH₂CH₂)_(n)OH, and n is an integer(e.g., 2 to 20, 5 to 15, or 10 to 12) (e.g., X═—(OCH₂CH₂)_(n)OH,R=poly(propylene glycol), and n=10 to 12) and Y—R—(OCH₂CH₂)_(n)OH, whereR=alkyl, aryl, or poly(propylene glycol), Y=a fluorinated moiety(perfluorinated alkyl or perfluorinated ether) or poly(ethylene glycol)capped with a fluorinated moiety, and n is an integer (e.g., 2 to 20, 5to 15, or 10 to 12) (e.g., Y=poly(ethylene glycol) capped with aperfluorinated alkyl group, R=poly(propylene glycol), and n=10 to 12).

In Comparative Example 1, the imprint resist was disposed directly onthe adhesion layer of a nanoimprint lithography substrate. FIG. 13 is animage of drops 1300 of the imprint resist on the adhesion layer 1302 ofa substrate 1.7 sec after dispensation of the drops in a lattice patternwas initiated. As seen in the image, drops 1300 have spread outward fromthe target areas on the substrate. However, spreading beyond the targetarea was limited, and the area of the exposed adhesion layer 1302exceeded that of drops 1300. Rings visible in this and other images,such as ring 1304, are Newton interference rings, which indicate adifference in thickness in various regions of the drop. Resist drop sizewas approximately 2.5 pL. FIG. 13 has a 2×7 (pitch)² interleaved latticeof drops (e.g., 2 units in the horizontal direction, with 3.5 unitsbetween the lines). Each following line shifted 1 unit in the horizontaldirection.

In Examples 1-3, pretreatment compositions A-C, respectively, weredisposed on a nanoimprint lithography substrate to form a pretreatmentcoating. Drops of the imprint resist were disposed on the pretreatmentcoatings. FIGS. 14-16 show images of the composite coating afterdispensation of drops of the imprint resist was initiated. Althoughintermixing occurs between the pretreatment composition and imprintresist in these examples, for simplicity, the drops of imprint resistand pretreatment coating are described below without reference tointermixing. The pretreatment composition was disposed on a wafersubstrate via spin-on coating. More particularly, the pretreatmentcomposition was dissolved in PGMEA (0.3 wt % pretreatmentcomposition/99.7 wt % PGMEA) and spun onto the wafer substrate. Uponevaporation of the solvent, the typical thickness of the resultantpretreatment coating on the substrate was in the range from 5 nm to 10nm (e.g., 8 nm). Resist drop size was approximately 2.5 pL in FIGS.14-16. FIGS. 14 and 16 have a 2×7 (pitch) interleaved lattice of drops(e.g., 2 units in the horizontal direction, with 3.5 units between thelines). Each following line shifted 1 unit in the horizontal direction.FIG. 15 shows a 2×6 (pitch) interleaved lattice of drops. The pitchvalue was 84.5 μm. The ratios of the volumes of resist to thepretreatment layer were in the range of 1 to 15 (e.g., 6-7).

Table 1 lists the surface tension (air/liquid interface) for thepretreatment compositions A-C and the imprint resist used in Examples1-3.

TABLE 1 Surface Tension for Pretreatment Compositions PretreatmentImprint resist Difference in Exam- Pretreatment surface tension surfacetension surface tension ple composition (mN/m) (mN/m) (mN/m) 1 A(Sartomer 34 33 1 492) 2 B (Sartomer 36.4 33 3.1 351HP) 3 C (Sartomer39.9 33 6.9 399LV)

In Example 1, drops of the imprint resist were disposed on a substratehaving a coating of pretreatment composition A (Sartomer 492 or“SR492”). SR492, available from Sartomer, Inc. (Pennsylvania, US), ispropoxylated (3) trimethylolpropane triacrylate (a multifunctionalacrylate). FIG. 14 shows an image of drops 1400 of the imprint resist onpretreatment coating 1402 and the resulting composite coating 1404 1.7seconds after dispensation of the discrete portions in an interleavedlattice pattern was initiated. In this example, the drop retains itsspherical cap-like shape and the spreading of the imprint resist islimited. As seen in FIG. 14, while spreading of the drops 1400 exceedsthat of the imprint resist on the adhesion layer in Comparative Example1, the drops remain separated by pretreatment coating 1402, which formsboundaries 1406 around the drops. Certain components of the imprintresist spread beyond the drop centers, forming regions 1408 surroundingdrops 1400. Regions 1408 are separated by pretreatment coating 1402. Thelimited spreading is attributed at least in part to the small differencein surface tension (1 mN/m) between pretreatment composition A and theimprint resist, such that there is no significant energy advantage forspreading of the drops. Other factors, such as friction, are alsounderstood to influence the extent of spreading.

In Example 2, drops of the imprint resist were disposed on a substratehaving a coating of pretreatment composition B (Sartomer 351HP or“SR351HP”). SR351HP, available from Sartomer, Inc. (Pennsylvania, US),is trimethylolpropane triacrylate (a multifunctional acrylate). FIG. 15shows images of drops 1500 of the imprint resist on pretreatment coating1502 and the resulting composite coating 1504 1.7 sec after dispensationof the drops in a square lattice pattern was initiated. After 1.7 sec,drops 1500 cover the majority of the surface area of the substrate, andare separated by pretreatment coating 1502, which forms boundaries 1506around the drops. Drops 1500 are more uniform than drops 1400 of Example1, and thus significant improvement is observed over the spreading inExample 1. The greater extent of spreading is attributed at least inpart to the greater difference in surface tension (3.1 mN/m) betweenpretreatment composition B and the imprint resist than pretreatment Aand the imprint resist of Example 1.

In Example 3, drops of the imprint resist were disposed on a substratehaving a coating of pretreatment composition C (Sartomer 399LV or“SR399LV”). SR399LV, available from Sartomer, Inc. (Pennsylvania, US),is dipentaerythritol pentaacrylate (a multifunctional acrylate). FIG. 16shows an image of drops 1600 of the imprint resist on pretreatmentcoating 1602 and the resulting composite coating 1604 1.7 sec afterdispensation of the drops in a triangular lattice pattern was initiated.As seen in FIG. 16, drops 1600 are separated at boundaries 1606 bypretreatment coating 1602. However, most of the imprint resist isaccumulated at the drop boundaries, such that most of the polymerizablematerial is at the drop boundaries, and the drop centers aresubstantially empty. The extent of spreading is attributed at least inpart to the large difference in surface tension (6.9 mN/m) betweenpretreatment composition C and the imprint resist.

Defect density was measured as a function of prespreading time for theimprint resist of Examples 1-3 and pretreatment composition B of Example2. FIG. 17 shows defect density (voids) due to non-filling of thetemplate. Plot 1700 shows defect density (number of defects per cm²) asa function of spread time (sec) for 28 nm line/space pattern regions,with the defect density approaching 0.1/cm² at 0.9 sec. Plot 1702 showsdefect density (number of defects per cm²) as a function of spread time(sec) over the whole field having a range of feature sizes with thedefect density approaching 0.1/cm² at 1 sec. By way of comparison, withno pretreatment, a defect density approaching 0.1/cm² is typicallyachieved for the whole field at a spread time between 2.5 sec and 3.0sec.

Properties of pretreatment compositions PC1-PC9 are shown in Table 2. Akey for PC1-PC9 is shown below. Viscosities were measured as describedherein at a temperature of 23° C. To calculate the diameter ratio (Diam.Ratio) at 500 ms as shown in Table 2, drops of imprint resist (drop size˜25 pL) were allowed to spread on a substrate coated with a pretreatmentcomposition (thickness of about 8 nm to 10 nm) on top of an adhesionlayer, and the drop diameter was recorded at an elapsed time of 500 ms.The drop diameter with each pretreatment composition was divided by thedrop diameter of the imprint resist on an adhesion layer with nopretreatment composition at 500 ms. As shown in Table 2, the dropdiameter of the imprint resist on PC1 at 500 ms was 60% more than thedrop diameter of imprint resist on an adhesion layer with nopretreatment coating. FIG. 18 shows drop diameter (μm) as a function oftime (ms) for pretreatment compositions PC1-PC9. Relative etchresistance is the Ohnishi parameter of each pretreatment compositiondivided by the Ohnishi parameter of the imprint resist. Relative etchresistance of PC1-PC9 (the ratio of etch resistance of the pretreatmentcomposition to the etch resistance of the imprint resist) is shown inTable 2.

TABLE 2 Properties of Pretreatment Compositions PC1-PC9 SurfaceViscosity Diam. Pretreatment Tension (cP) Ratio Rel. Etch Composition(mN/m) at 23° C. at 500 ms Resistance PC1 36.4 ± 0.1 111 ± 1  1.59 1.3PC2 37.7 ± 0.1 66.6 ± 0.3 1.86 1.5 PC3 33.9 ± 0.1 15.5 ± 0.1 2.46 1.1PC4 41.8 ± 0.1 64.9 ± 0.3 1.92 1.9 PC5 38.5 ± 0.3 18.4 ± 0.1 2.73 1.7PC6 NA NA 1.75 0.9 PC7 35.5 ± 0.3  8.7 ± 0.1 2.36 1.1 PC8 39.3 ± 0.110.0 ± 0.1 2.69 0.9 PC9 38.6 ± 0.1 143 ± 1  1.95 0.9 Imprint 33 1.00 1.0Resist PC1: trimethylolpropane triacrylate (Sartomer) PC2:trimethylolpropane ethoxylate triacrylate, n ~1.3 (Osaka Organic) PC3:1,12-dodecanediol diacrylate PC4: poly(ethylene glycol) diacrylate, Mn,avg = 575 (Sigma-Aldrich) PC5: tetraethylene glycol diacrylate(Sartomer) PC6: 1,3-adamantanediol diacrylate PC7: nonanediol diacrylatePC8: m-xylylene diacrylate PC9: tricyclodecane dimethanol diacrylate(Sartomer)

Pretreatment compositions PC3 and PC9 were combined in various weightratios to yield pretreatment compositions PC10-PC13 having the weightratios shown in Table 3. Comparison of properties of PC3 and PC9 withmixtures formed therefrom revealed synergistic effects. For example, PC3has relatively low viscosity and allows for relatively fast templatefilling, but has relatively poor etch resistance. In contrast, PC9 hasrelatively good etch resistance and film stability (low evaporativeloss), but is relatively viscous and demonstrates relatively slowtemplate filling. Combinations of PC3 and PC9, however, resulted inpretreatment compositions with a combination of advantageous properties,including relatively low viscosity, relatively fast template filling,and relatively good etch resistance. For example, a pretreatmentcomposition having 30 wt % PC3 and 70 wt % PC9 was found to have asurface tension of 37.2 mN/m, a diameter ratio of 1.61, and an Ohnishiparameter of 3.5.

TABLE 3 Composition of Pretreatment Compositions PC10-PC13 PretreatmentPC3 PC9 Composition (wt %) (wt %) PC10 25 75 PC11 35 65 PC12 50 50 PC1375 25

FIG. 19A shows a plot of viscosity for pretreatment compositionsincluding various ratios of PC3 and PC9 (i.e., from 100 wt % PC3 to 100wt % PC9). FIG. 19B shows drop diameter (measured as described withrespect to Table 2) for PC3, PC13, PC12, PC11, PC10, and PC9. FIG. 19Cshows surface tension (mN/m) versus fraction of PC3 and PC9.

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made without departing fromthe spirit and scope of the disclosure. Accordingly, other embodimentsare within the scope of the following claims.

What is claimed is:
 1. A nanoimprint lithography method comprising:disposing a pretreatment composition on a nanoimprint lithographysubstrate to form a pretreatment coating on the nanoimprint lithographysubstrate, wherein the pretreatment composition comprises apolymerizable component; disposing discrete portions of imprint resiston the pretreatment coating, each discrete portion of the imprint resistcovering a target area of the nanoimprint lithography substrate, whereinthe imprint resist is a polymerizable composition and comprises apolymerization initiator; forming a composite polymerizable coating onthe nanoimprint lithography substrate as each discrete portion of theimprint resist spreads beyond its target area, wherein the compositepolymerizable coating comprises a mixture of the pretreatmentcomposition and the imprint resist; contacting the compositepolymerizable coating with a nanoimprint lithography template;activating the polymerization initiator; polymerizing the compositepolymerizable coating to yield a composite polymeric layer and anuncured portion of the pretreatment coating on the nanoimprintlithography substrate; and after polymerizing the compositepolymerizable coating to yield the composite polymeric layer,polymerizing the uncured portion of the pretreatment coating, whereinthe polymerization initiator comprises a first photoinitiator, andpolymerizing the composite polymerizable coating comprises initiatingpolymerization of the composite polymerizable coating by irradiating thecomposite polymerizable coating with UV radiation of a first wavelength,intensity, energy density, and duration.
 2. The nanoimprint lithographymethod of claim 1, wherein the pretreatment composition is substantiallyfree of a polymerization initiator.
 3. The nanoimprint lithographymethod of claim 2, wherein polymerizing the uncured portion of thepretreatment coating comprises irradiating the uncured portion of thepretreatment coating with UV radiation of the first wavelength and asecond intensity, energy density, duration, or combination thereof,wherein at least one of the second intensity, energy density, orduration differs from that of the first and is sufficient to initiateautopolymerization of the uncured portion of the pretreatmentcomposition.
 4. The nanoimprint lithography method of claim 1, whereinthe pretreatment composition comprises a thermal initiator.
 5. Thenanoimprint lithography method of claim 4, wherein polymerizing theuncured portion of the pretreatment coating comprises heating theuncured portion of the pretreatment coating to a temperature and for aduration sufficient to initiate polymerization of the uncured portion ofthe pretreatment coating.
 6. The nanoimprint lithography method of claim1, wherein the pretreatment composition comprises the firstphotoinitiator.
 7. The nanoimprint lithography method of claim 6,wherein the imprint resist comprises a photosensitizer.
 8. Thenanoimprint lithography method of claim 7, wherein polymerizing theuncured portion of the pretreatment coating comprises irradiating theuncured portion of the pretreatment coating with UV radiation of thefirst wavelength and a second intensity, energy density, duration, orcombination thereof, wherein at least one of the second intensity andenergy density exceeds that of the first.
 9. The nanoimprint lithographymethod of claim 1, wherein the pretreatment coating comprises a secondphotoinitiator, wherein the second photoinitiator is different from thefirst photoinitiator.
 10. The nanoimprint lithography method of claim 9,wherein polymerizing the uncured portion of the pretreatment coatingcomprises irradiating the uncured portion of the pretreatment coatingwith UV radiation of a second wavelength, wherein the second wavelengthis shorter than the first wavelength.
 11. The nanoimprint lithographymethod of claim 9, wherein polymerizing the uncured portion of thepretreatment coating comprises irradiating the uncured portion of thepretreatment coating with UV radiation of a second wavelength and asecond intensity, energy density, or duration, wherein the secondwavelength is shorter than the first wavelength, and at least one of thesecond intensity and energy density exceeds that of the first.
 12. Thenanoimprint lithography method of claim 9, wherein polymerizing theuncured portion of the pretreatment coating comprises irradiating theuncured portion of the pretreatment coating with UV radiation of asecond intensity, energy density, or duration, wherein at least one ofthe second intensity or energy density exceeds that of the first. 13.The nanoimprint lithography method of claim 1, wherein activating thepolymerization initiator does not initiate polymerization of thepretreatment composition.